Voting opened in the crucial Democratic primary in the American state of Pennsylvania, where Hillary Clinton is favoured to win against front-runner Barack Obama but she is unlikely to overtake his overall lead in her quest for the party's Presidential nomination.
The state could play a decisive role in what has become an increasingly bitter fight for the Democratic nomination for the November presidential polls.
At stake are 158 pledged delegates that the state will send to the party convention in Denver in August to choose the nominee to fight against presumptive Republican candidate John McCain.
61-year-old Clinton, the New York Senator, is running ahead and needs to win big to impress the donors and super delegates - elected party functionaries and leaders - who will have the final say if neither candidate wins a majority of pledged delegates, a scenario most likely to play out.
Besides, her performance would be closely watched by major donors who in recent weeks are shying away form her. Should Obama, 47, spring a surprise and win a majority of delegates, it could signal the end of Clinton's campaign.
As the campaign neared end, Clinton launched a controversial television advertisement which invoked images of Osama bin Laden -- mastermind of September 11 2001 attacks on New York and Washington, attack on Pearl Harbour by Japanese in the Second World War and devastation caused by hurricane Katrina to press the point that Obama cannot lead the country effectively in a major crisis.
Obama, who had questioned Clinton's links to big businesses and lobbyists in Washington, did not directly reply to the advertisement but his campaign hit back, accusing her of engaging in "politics of fear" like President George Bush.
Fear would not help unite the country in the times of crises, Obama's campaign said.
However, Clinton, in a TV interview, rejected the contention that she is employing the politics of fear to win and said her advertisement was just trying to depict the reality.
She has all along contended that Obama lacks experience to lead the country as President and Commander-in Chief and that she is best suited for the job having been in Washington for several years as first lady and Senator.
But Obama asserts that he is seeking to change the "business as usual" in Washington where big corporation prevails and cites Clinton's connections with big businesses and lobbyists to stress that she would not be able to bring about the change that American people want.
The polling will close at 2000 hours (0530 IST tomorrow) in the election in which only registered Democrats can vote. In the US, a person can register as Democrat or Republican or independent but is not obliged to vote for the party.
Obama, who found good support among the young, had launched a campaign to get new voters registered ahead of primary and polls place him in strong position in Philadelphia and surrounding area, but Clinton is projected to be leading in the rest of the state.
In the dying hours of campaign, Clinton urged voters not to cast their ballot on faith or guess work as she sought to project that she had experience and toughness needed to lead the country.
Even in the best case scenario, she is not expected to wipe out the deficit of pledged delegates against Obama and the battle in all probability would move on to Indiana and North Caroline where primaries are due on May 6.